Bump sphinx from 4.0.2 to 4.0.3

Bumps [sphinx](https://github.com/sphinx-doc/sphinx) from 4.0.2 to 4.0.3.
- [Release notes](https://github.com/sphinx-doc/sphinx/releases)
- [Changelog](https://github.com/sphinx-doc/sphinx/blob/4.x/CHANGES)
- [Commits](sphinx-doc/sphinx@v4.0.2...v4.0.3)

---
updated-dependencies:
- dependency-name: sphinx
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

Signed-off-by: dependabot[bot] <support@github.com>

docs/requirements.txt

@@ -1,3 +1,3 @@
-sphinx==4.0.2
+sphinx==4.0.3
 sphinx_rtd_theme==0.5.2
 m2r2==0.2.8